The Intensity Profile of the Solar Supergranulation

TL;DR

This study measures the average radial intensity profile of solar supergranulation, revealing a slight brightness decrease from cell centers to boundaries, and discusses potential causes including magnetic flux variations and thermal effects.

Contribution

It provides the first detailed measurement of the supergranular intensity profile and explores its possible physical origins, including magnetic and thermal influences.

Findings

Approximately 0.1% decrease in intensity from center to boundary

Corresponds to about 1.0 K brightness temperature decrease

Magnetic flux elements may influence supergranular scale selection

Abstract

We have measured the average radial (cell center to network boundary) profile of the continuum intensity contrast associated with supergranular flows using data from the Precision Solar Photometric Telescope (PSPT) at the Mauna Loa Solar Observatory (MLSO). After removing the contribution of the network flux elements by the application of masks based on Ca II K intensity and averaging over more than 10^5 supergranular cells, we find a ~ 0.1% decrease in red and blue continuum intensity from the supergranular cell centers outward, corresponding to a ~ 1.0 K decrease in brightness temperature across the cells. The radial intensity profile may be caused either by the thermal signal associated with the supergranular flows or a variation in the packing density of unresolved magnetic flux elements. These are not unambiguously distinguished by the observations, and we raise the possibility that the network magnetic fields play an active role in supergranular scale selection by enhancing the radiative cooling of the deep photosphere at the cell boundaries.